LCD Panels for CM-X255

CompuLab provides the following means for evaluating and adapting LCD panels:

  • Ready for use panel, including cable and s/w setup. Panel: LG/Philips LP064V1 (or similar), 640 x 480, TFT color, 6.4″.
  • The list of verified panels, including ready for use setups for some of them.
  • Generic driver and configuration files enabling adaptation of a new panels.
  • Verification and adaptation service performed by CompuLab.

Generic Driver and Configuration Files

The generic driver enables application programs to access the specified LCD panel as a standard display. CompuLab provides configuration files for driver’s setup, per supported operating system. Configuration file has to be compiled into operating system.

Panel Compatibility Verification

CompuLab provides a service for verification of specific panel’s compatibility to the CORE’s graphics controller. The service works as follows:

  1. The user selects a panel which meets his requirements.
  2. The panel’s datasheet is emailed to CompuLab.
  3. CompuLab’s engineers compare the panel’s datasheet with the graphics controller specifications and reply with compatibility comments.

The verification service is provided for buyers of evaluation kit, and is limited to 3 panels.

Adaptation Service by CompuLab

CompuLab also provides a service of LCD panel adaptation: CompuLab configures the generic driver to support a particular LCD panel, whose compatibility was previously verified. Configured driver has to be compiled by the user and linked with operating system.

Required User’s Actions and Tools

While technical part of solution is provided by CompuLab, user still needs several additional steps to accomplish the task. In case of Linux, the configuration file should be compiled with the kernel. User needs Linux compilation tool chain and kernel drivers kit, both can be downloaded from CompuLab’s web-site.

In case of Win CE, user has to rebuild the image including the new panel support. Platform Builder from Microsoft and Win CE Drivers Kit from CompuLab should be obtained to accomplish the task.

Guidelines for LCD panel Selection

Graphics controller used in CM-X255 is implemented within PXA255 processor. It is compatible with most panels available in the market. Final selection should be confirmed by CompuLab. Selection guidelines:

Panel Type / Interface Monochrome, TFT or STN / DSTN ( 4,8,16 bit )
ResolutionUp to 1024 x 768
Bits per pixel (max)Up to 16

Panels with resolutions lower than 320 x 240 are supported by graphics controller, however they sometimes require complicated adaptation, in which case CompuLab reserves the right to refuse adaptation service.

> Verified Panels List

Limitations of Display Controller Capabilities

Based on Intel’s PXA255 SoC, the display controller of the CM-X255 provides a cost-efficient solution for the requirements of a typical embedded application. However, display capabilities are traded with cost-effectiveness to a certain extent, which is translated into limitations requiring a user’s awareness.

The display controller shares memory bandwidth with other on-board functions using the local bus. When the bit rate is high and the bus is locked by another device, the display FIFO may reach the underrun state, thereby disturbing the displayed image. The disturbance has been significantly reduced in the latest version of CM-X255 (version 3), by modifying the bus arbitration logic and by changing the bus interface of the Ethernet controller.

Possible sources of disturbance:

  • Peripherals located in the Super-IO chip – PS/2 keyboard and mouse interface, parallel port and COM-D serial port.
  • Host USB ports
  • Off-board devices on LPC and PCI busses. (There are no on-board devices connected to the PCI bus)

Disturbance level heavily depends on the display’s bit rate and panel type. STN panels are not affected at all. TFT panels at resolutions lower than or equal to 640 x 480 x 8-bit practically don’t exhibit disturbance either. At higher resolutions, the display quality depends on the activity level of the above-mentioned sources. If the disturbance sources aren’t active, resolutions such as 640 x 480 x 16 or even 800 x 600 x 16 are displayed well.

Taking into account the requirements of a typical embedded design, the display quality has been found satisfactory in almost all cases.

Using CRT and Flat Panel Monitors

On CRT and Flat Panel monitors with analog RGB interface, the disturbance is significant, because they don’t use pixel clock input (in contrast to LCD panels). Monitors regenerate the pixel clock from sync pulses, which makes them more sensitive to short distractions.

Flat Panel monitors are especially sensitive, and therefore are barely compatible with the graphics capabilities of the CM-X255. A user is advised to avoid the following combination: [Flat Panel monitor] + [Graphics resolution above 640 x 480 x 8] +  [PS/2 keyboard/mouse], unless it is used only in the development stage, when display quality is not critical.

Limitations of Flat Panel monitors’ usage apply only for monitors with an analog RGB interface. Monitors with newer DVI interface are less sensitive, similar to regular LCD panels.